@JoeX I encounter the same disappointment with BBS:
I did a triathlon last year in the Pyrénées. For the Bike split, I used BBS to estimate my time. Previously, I tried to nail my Cda running their Race Analytic tools. Despite following the recommended target power, I ended with an extra 20’ minutes (4h vs 3h40).
After the race, I ran again the race Analytic tools to adjust my Cda, rerun the race plan with the exact NP of the race. It still gave me a 20’ minutes difference with my actual race time.
DId the same exercise this year and it got even worth: the time difference jump up to 30 minutes…
I asked BBS for help and the only answer was that I did not properly follow the power plan, which I can’t really .check - anyone has a tool to compare the power files ?.
One key element: this was in a very mountainous environment, meaning complex winds and snicky roads. So I can understand the difficulty to nail the data model… On other races, this estimates were closer to the actual time.
I don’t think it will help you but at least you know that you’re not alone… 